1. Field of the Invention
The present invention relates to a copying apparatus and a copying method, and more specifically, a copying apparatus and a copying method for copying an original image onto a copy sheet in the electrophotographic method.
2. Description of Related Art
Generally, in an electrophotographic copying machine, an original is scanned and exposed to light by the movement of an optical system, and it is necessary to change originals on an original glass one by one. In order to omit this troublesome operation, the changing of originals and to improve the efficiency of such a copying machine, various types of automatic document feeders (which is hereinafter referred to as ADF) have been developed. An original-moved scanning type of ADF wherein an original is scanned by an optical system standing by at a scan starting position while being transported at a fixed speed so that the image is projected onto a photosensitive drum has been suggested as type of ADF.
Incidentally, in the original-moved scanning type of ADF, the transport of an original by the ADF to a position where the original is exposed to light from an optical system needs to be synchronized with the supply of a copy sheet to a transfer section so that the leading edge of the image formed on the photosensitive drum agrees with the leading edge of the copy sheet. However, when the optical system returns to a scan starting position in an ordinary image exposure operation, it never returns exactly to the scan starting position and comes to a standstill, slightly overrunning the position. Further, the overrun distance is different from scan to scan. If a copying operation is performed using the ADF regardless of the overrun distance, an image is copied onto a copy sheet, lagging in the direction of the travel of copy sheets according to the overrun distance.
Conventionally, the different positions where the optical system comes to a standstill in every scan are measured by exclusive detection means, and based on the measured value, the transport of an original and the supply of a copy sheet are adjusted in order to synchronize them. In this way, however, the installation of the exclusive detection means is costly, and the regulation is complicated.